1. Field of the Invention
This application is based upon and claims the benefit of priority from Japanese patent application No. 2006-211256, filed on Aug. 2, 2006, the disclosure of which is incorporated herein in its entirety by reference.
The present invention relates to a reflection plate and a liquid crystal display device and, in particular, to a reflection plate including an uneven pattern and to a liquid crystal display device of typically a transflective or reflective type, which comprises such reflection plate.
2. Description of the Related Art
With typical transmissive liquid crystal display devices such as those used for displays or monitors of notebook personal computers, it is hard to view the display in the open airs under the strong sunlight due to the light reflected by the surface of the liquid crystal display device. Therefore, transflective liquid crystal display devices have recently been employed in many cases for display units of mobile apparatuses such as mobile telephones, and digital video cameras, digital cameras, etc. The transflective liquid crystal display device uses the backlight as the light source indoors and uses the surrounding light such as the sunlight as the light source outdoors. Thus, the display can be finely viewed so that it is optimum as the displays of the mobile apparatuses or cameras. Further, the reflective liquid crystal display devices which exhibit low power consumption using no backlight are also used widely for portable game machines and the like.
Such transflective or reflective liquid crystal display device uses a reflection plate for reflecting the surrounding light. For providing the reflection plate, generally employed is a method which provides an uneven pattern inside the panel of the liquid crystal display device by using a photosensitive organic film (for example, see Japanese Unexamined Patent Publication S58-125084, pp. 4-7 and FIG. 1 (Patent Document 1) and Japanese Unexamined Patent Publication H4-243226, pp. 3-5 and FIG. 1 (Patent Document 2)). The reason for this is that: such method has a great affinity with the process (in particular, with photolithography process using resist) for fabricating a TFT (thin film transistor)-type liquid crystal display device; the process for forming the reflection plate can be achieved at a low cost; and the reflective property obtained thereby is more excellent than those obtained through other methods for forming the unevenness.
If the unevenness exhibits high regularity in such liquid crystal display device with the reflection plate including the uneven pattern, the surface of the liquid crystal display device looks shining in rainbow hues due to the interference effect of the light when strong light such as the direct sunlight is irradiated thereto. Such phenomenon becomes critical for mobile apparatuses and the like which are often used outdoors as well. Therefore, there have been various measures proposed to be taken to deal with such shortcomings.
Generation of the interference mentioned above is deeply related to the periodicity of the uneven patterns, and rainbow-like coloring is generated because the interference has the dependency on the wavelengths of the light. Thus, it is possible to lighten the interference through making the uneven pattern random, etc. For example, Japanese Unexamined Patent Publication H8-184846, pp. 3-6 and FIG. 1 (Patent Document 3) discloses a method for arranging the unevenness of the reflection plate irregularly. Further, Japanese Unexamined Patent Publication H11-337964 (Patent documents 4) and Japanese Unexamined Patent Publication 2002-142115 (Patent documents 5) disclose specific designing methods of the unevenness.
Among those, Patent Document 4 discloses a method which arranges the uneven pattern randomly and arranges the center of a recessed part or a protruded part of an uneven scatter reflection electrode at each lattice point of a tetragonal lattice or a closest-packed lattice except for a part of the lattice points. When the lattice point is actually moved randomly, there are cases where the neighboring recessed parts or the protruded parts overlap with each other as shown in FIG. 13, and the area of the overlapped protruded or recessed part becomes too large. Thus, the shape obtained thereby becomes more flattened than a desired shape, and the area effective for scattering the light is decreased. In the meantime, as shown in FIG. 3 of Patent Document 4, if the lattice points are moved randomly in such a manner that the neighboring recessed parts or protruded parts do not overlap with each other, interference of the reflected light cannot be suppressed sufficiently.
Meanwhile, Patent Document 5 discloses a method which arranges at least a part of the recessed parts or the protruded parts substantially in a helical form or substantially in a radial form. With this method, regulation of the layout is effective when there are a large number of protruded parts or the recessed parts (that is, when the uneven part is extremely small with respect to a unit pixel of the liquid crystal display device as in examples provided later) as shown in FIG. 1 of Patent Document 5 (FIG. 15 of this Application of the present invention). However, recent liquid crystal display devices have been advanced to have high-definition, and the unit pixel has become still smaller. On the other hand, it has reached to a point where the uneven pattern cannot be reduced in size due to the limit in the photolithography used for forming the unevenness. Therefore, in the highly fine liquid crystal display device, the number of the protruded parts or the recessed parts formed at the unit pixels becomes automatically smaller. Thus, the layout disclosed in the above-described Patent Documents has no effect on reducing the interference.